1. Field of the Invention
The present invention relates to a switching regulator circuit that supplies power to be supplied to a load and a vehicular lamp used in a vehicle.
2. Description of the Related Art
Conventionally, a switching regulator circuit is provided between a power supply and a load, in order to control power to be supplied to the load as disclosed, for example, in Japanese Patent Application Laid-Open No. 2001-215913, pages 6-12 and FIGS. 2-6. The switching regulator circuit repeatedly switches whether or not the power is allowed to be supplied to the load, thereby controlling a duty ratio of a voltage and a current that are to be supplied to the load.
The switching regulator circuit generates a saw-tooth wave and switches whether or not the power is supplied to the load at a timing based on the result of comparison of a value of the thus generated saw-tooth wave with a predetermined threshold value. Moreover, the switching regulator circuit changes the threshold value with which the value of the saw-tooth wave is compared or changes the frequency of the saw-tooth wave and the threshold value with which the value of the saw-tooth wave is compared, thereby controlling the duty ratio of the voltage and current to be supplied to the load. The control of the frequency of the saw-tooth wave and the control of the threshold value are performed by using an integrated circuit.
According to the conventional method of controlling the duty ratio mentioned above, however, the integrated circuit for the control is required. This increases the cost of the switching regulator circuit. Especially, in a case of controlling a high voltage and a large current, an integrated circuit having the increased cost is required. Although a high-performance control circuit such as the integrated circuit is not required in a case where it is not necessary to perform the control with high precision, the conventional control method mentioned above requires the integrated circuit. However, the use of the integrated circuit did not provide effects that are worth the cost.